The COVID-19 epidemic, like all epidemics, is occurring because the disease is contagious enough that each infection, on average, results in 2 to 3 further infections. This process creates the exponential growth we have seen repeated across countries, states, and cities. Any successful intervention must reduce this number of secondary transmissions.
Current broad-scale social distancing interventions aim to bring this number down by decreasing the number of contacts between people across the population. These policies work because if people do not encounter each other, they cannot spread infection. But current social distancing policies ask all people to stay home, not just people who are likely to be sick. In this way, social distancing is a broad intervention, and we need it be this broad because we lack accurate estimates of who is infected.
The use of social distancing across the United States and many regions of the world reveals a gap in our outbreak response: we need broader surveillance of COVID-19 spread. A surveillance system is necessary both for measuring the effect of these broad interventions, and for making these containment policies more targeted. We need a robust surveillance system to guide social distancing policies and to adjust them based on the intensity of community spread.
Unfortunately, broad-scale social distancing is a blunt intervention with massive societal and economic costs.
If we can move toward a system where we ask only infected and exposed individuals to distance, we can achieve the same outcomes with less societal hardship.
The crux of that system is being able to find people who were exposed to the disease before they develop the disease. Contact tracing is a time-tested method for doing exactly this. By asking a confirmed case about people they interacted with while they were infectious, you can build a list of people who were exposed to the disease, and may become infectious themselves. By identifying those exposed individuals early, you can ask them to isolate and link them to testing before the spread the disease to others.
Contact tracing targets surveillance resources and testing at individuals most likely to be positive, and also serves to test individuals early in the course of illness when isolation is most effective at reducing transmission. Testing exposed individuals may also identify asymptomatic infections that would otherwise have gone undetected. However, traditional approaches to contact tracing do not scale.
Traditional approaches rely on a huge investment in time and labor on the part of public health staff. Experts must conduct thousands of hours of phone interviews, and each new confirmed case requires many hours of detailed followup.
Because of the effort required, contact tracing is typically only conducted in the early “containment” phase of an epidemic when there are fewer cases. Once widespread community transmission occurs, there are simply not enough resources to keep up.
Our work at present
Our first deliverable is a survey-based contact tracing platform that can be deployed by public health officials around the United States.
As our work matures
Beyond simply developing a system that can monitor individual-level interactions and exposure events, understanding high resolution transmission patterns on a broad scale would allow us to characterize the heterogeneity of the epidemic in different areas. While we are all facing the same disease, variable levels of immunity, population densities, and age structures will create subtly different environments for transmission. Therefore, in addition to guiding individual-level containment measures after exposure, we will use this platform to help inform containment policies at the community level.